Recently application of a device having a minute structure, which is formed by a micromachining technology, is developed in various technical fields. Examples of the device include micro movable devices, such as an angular velocity sensor, an acceleration sensor, and a micromirror element, which have minute movable units. For example, the angular velocity sensor and the acceleration sensor are applied to an image stabilizing function of a video camera or a camera-equipped mobile telephone, an automobile navigation system, an air-bag inflation timing system, an attitude control system such as of an automobile and a robot. For example, the micromirror element is used as an element that plays a light reflecting function in an optical disk technology or an optical communication technology.
Japanese Patent Application Laid-Open Nos. 2001-196484, 2005-251898, and 2008-207311 disclose a method in which, in a process for producing a device having a minute structure, packaging is performed at a wafer level in order to avoid adhesion of a foreign matter or dust to a device or damage of the device.
First a device wafer and a packaging wafer are prepared in order that the packaged device is produced while the wafer-level packaging is realized. The device wafer includes plural device forming partitions. The device is formed in each device forming partition. The packaging wafer is separated into plural packaging units. After various kinds of processing are performed to the device wafer and the packaging wafer, the device wafer and the packaging wafer are bonded. Before the bonding, the device is formed in each device forming partition of the device wafer. Before the bonding, on a surface of the packaging wafer, an insulating film is formed in a region to be bonded to the device wafer (this is because electric separation between the device and the packaging unit is achieved in the produced packaged device).
Japanese Patent Application Laid-Open Nos. 2007-201196 and 2007-324195 disclose a room-temperature bonding method as a bonding technique. In the room-temperature bonding method, a high-temperature process can be avoided in the bonding, and therefore a problem caused by the high-temperature process can be avoided.
However, conventionally, even if the device wafer and the packaging wafer are bonded by the room-temperature bonding method while the insulating film is interposed therebetween, the electric separation is insufficiently achieved between the device wafer and the packaging wafer, and sometimes the electric separation is insufficiently achieved between the device and the packaging unit base material in the obtained packaged device. When the electric separation is insufficiently achieved between the device and the packaging unit base material, frequently a desired characteristic is not obtained in the device.